My external device SSD not able to mount for my data files

[stevef]

Having a look at the logs may show what is happening as that error message is very general.  Assuming the SSD is in a USB caddy you could do something like this. 

Boot up your system and allow it to sit idle for a while so nothing is going on in the background.
Open a terminal with 'Ctrl Alt T'
Make a note of the system time in the HH:MM format e.g. 17:55
Connect the external SSD.
If it would normally auto-mount allow enough time for this to complete.
Otherwise attempt to mount it as normal e.g. right click and enter password etc

Once the mount operation has failed run these commands in the terminal.
Replace HH:MM with the value you noted earlier.

Code:

journalctl -b --since HH:MM

press space bar to page through the output (or enter to advance line by line) until you see (END), then q to exit

You may get extra information with this command

Code:

sudo dmesg

Edit to correct typing error.

In both cases, you may need to scroll up a bit to find the messages relating to the SSD connection and mount.
A message saying 'New USB device found' would be a typical place to start reviewing.
Check the messages after that and look for any relating to mount errors

Post back with the results if necessary.